Metal filament.



TED STATES PATENT OFFICE.

MATTHEW A. HUNTER OF SGHENECTADY, NEW YORK, ASSIGNOR TO GENERAL 'ELEC- TRIO COMPANY, A CORPORATION OF NEW YORK.

METAL FIIQAMENT.

No Drawing.

To all whom it may concern:

Be it known that I, MA'I'IHEW A. HUNTER, a subject of the King of Great-Britain, residing at Schenectady, county of Schenect'ady, State of New York, have invented cerv tain new and useful Improvements in Metal Filaments, of which the following is a.speci must be given to the filament to make it opfication. 4

Various refractory metals such as tantalum, have heretofore been proposed as suitable materials for lamp filaments and other conductors subject 'to high temperatures.

-One difficulty in the use of some of these refractory elements-arises from the low specific resistance. of the materialand the consequent length and small cross-section which of, say 15 mm. This heating ,causes a chemi cal reaction between the nitrogen and art of the tantalum, probably with the'production of tantalum-.nitrid. The resistance of the filament is greatly increased and a filament which when cold has a resistance of 65 ohms before treatment, may have a cold resistance as high as240 ohms after treatment lasting about one minute.

.l'do'notwish to advance any theory astowhy the treatment with nitrogen increases Specification of Letters Patent.

- Application filed July 2, 1906. Serial No. 324,410.-

E Patented Apr. 16, 1912.

the resistance of the filament, but I have found that such is the case and that a filament-after treatment may .be run with a brilliancy apparently equal to that of the untreated tantalum filament.

One great advantage in using my process is that the finished filaments may be much thicker, for a given voltage, than filaments of the pure metal, or, stating the principlein a difierent way, the filaments ,may be much shorter for a given cross-section.

What I claim as new and desire to secure by Letters Patent'of the United States, is, 1.' The process which consists in heating a filament of substantially pure tantalum in an atmosphere of nitrogen, to cause chemical reaction between ,the nitrogen and the tantalum and thereby increase the electrical resistanceof the filament. K

2. The process which consists in glowing a tantalum filament in an atmosphere of nitrogen to increase the specific resistance of the filament.

3. A filament consisting substantially of tantalum, but having a specific resistance higher than that of pure tantalum because ofthe presence ofa nitrogen compound.

. 4. A tantalum filament containing mate'- rial produced by glowing said filament in an atmosphere of nitrogen, said filament hav-.

ing a specific resistance higher than that of pure metal.

In' 'tness.whereof,I have hereunto set my hand this 30th day of J une,1906.

. MATTHEW AJHUNTER; Witnesses: I

A EDWARD WILLIAMS, Jr., ABBA B. MARVIN, Jr. 

